Abstract

Soccer manufacturers are investing significant amounts of time and money researching and developing soccer balls, using advanced materials and constructions in an attempt to create a ball that has better flight and impact characteristics. An important consideration in any structure subject to dynamic or impact loading is its mechanical response. The recent development of non-contact optical vibration measurement tools such as the SLDV have made the measurement of such responses a more realistic possibility. The technique of vibrometry utilises the Doppler principle to provide a measure of the surface velocity at the point at which a laser beam is incident. The SLDV benefits from its non-contact and non-marking method and the speed and ease with which measurements can be recorded. This paper reports the method and results from a study aimed at determining the dynamic responses of two different soccer balls. The balls are excited using either an acoustic source or mechanical shaker and the velocity of each ball's surface at a series of points is recorded. The natural frequencies and vibration mode shapes are identified and a comparison is made between the responses of each ball. Significant mode shapes were observed between 50 Hz and 1400 Hz. At the lower frequencies the mode shapes were observed to be independent of the outer panels, based more on the structure of the ball as a whole, at the higher frequencies the mode shapes were centred on individual panel oscillations. The soccer balls tested show some noticeable differences in mode shapes. Verf.-Referat